Galvanic action device for scuttling floating objects



March 7, 1967 A. c. SULESKI 3,308,046

GALVANIC ACTION DEVICE FOR SCUTTLING FLOATING OBJECTS Filed Feb. 6, 1963 ELECTROLYTE 280 28b 28c 28d 25 24 FIG. 3b

United States Patent ll 3,308,046 GALVANIC ACTION DEVICE FOR SCUTTLIN G FLOATING OBJECTS Anthony C. Suleski, Centerport, N.Y., assignor to Hazeltine Research, Inc., a corporation of Illinois Filed Feb. 6, 1963. Ser. No. 256,562 8 Claims. (Cl. 204196) GENERAL The present invention relates to a galvanic action device and a number of techniques for controlling the flow of galvanic corrosion current to compensate for any changes in this current which tend to be developed by changes in the physical characteristics of an electrolyte in which the galvanic action device is immersed. The invention is particularly useful for scuttling a floating object at a prescribed time and will be described in this environment.

In many naval operations, electronic detection equipment is deposited in the ocean to obtain information about any objects such as submarines lying beneath the surface. In any such operation, it is necessary either to remove the equipment from the water or scuttle it after it has served its purpose. The primary reason for doing this is to prevent the enemy from locating the equipment and picking it up. In addition, because so many of these pieces of detection eouipment are deposited in the ocean, it is necessary that they be removed in order to prevent them from interfering with shipping.

It has been found to be more practical to scuttle these pieces of equipment after they have performed their function rather than retrieve them. Thus, it is necessary to use a reliable scuttling device to ensure that the object will scuttle at the desired time.

Various scuttling techniques are presently being used but all suffer from one or more shortcomings. One device presently in use is a salt plug formed of compacted salt. Such a salt plug is placed in the outer surface of the detection equipment and is intended to dissolve in the sea water at a particular time thus permitting the sea Water to enter the floating object for scuttling. It has been found that this salt plug is unreliable in that the scuttling times for a number of them may vary over a relatively wide range. This lack of reliability may be due to either the imperfect manufacturing process by which they are produced or the fact that salt is susceptible to moisture, so instead of dissolving, the salt may form a hydrate which makes it more difficult to dissolve.

A second scuttling device, known as a souib, uses an explosive which is set off at the prescribed time. The explosion punctures the outer surface of the detection equipment thereby permitting the sea water to enter the object for scuttling. The squib has been found to be relatively expensive and such a factor becomes important when these devices are manufactured on a large scale. A further problem with the squib is that the explosive makes it delicate to handle. Thus, the explosive creates handling problems both on the production line and en route to the point at which the electronic equipment is deposited in the ocean.

Other types of scuttling devices utilizing a combination of mechanical and chemical principles are also presently in use. These devices suffer from the shortcoming that they are intricate and complex in construction and are therefore likely to be relatively expensive and subject to frequent breakdowns.

It is an object of the present invention to provide a new and improved galvanic action device.

It is another object of the present invention to provide a new and improved galvanic action device for scuttling a floating object at a prescribed time.

It is a further object of the present invention to provide 3,308,046 Patented Mar. 7, 1967 a new and improved galvanic action device which is simple in construction, inexpensive to fabricate and reliable for scuttling a floating object at a prescribed time.

A galvanic action device constructed in accordance with the present invention comprises a galvanic cell which develops a corrosion current having a magnitude dependent upon the physical characteristics of an electrolyte in which the cell is immersed and means for governing the corrosion current to compensate for changes in the current which tend to be developed by the physical characteristics.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, FIGS. 1, 2 and 3 each show different embodiments of the present invention.

Galvanic action generally Whenever a metal is exposed to air or a liquid, normal corrosion of the metal takes place. When such a metal is placed in electrical contact with another more noble metal, for example, when both metals are immersed in the same corroding solution called an electrolyte, an accelerated electrochemical corrosion is produced on the less noble metal, that is, on that metal more conductive to corrosion. This accelerated corrosion results in a protection from corrosion for the more noble metal. Galvanic corrosion is generally understood to consist of the total corrosion of the less noble metal. Thus, galvanic corrosion of a metal comprises the normal corrosion'of the metal due to exposure alone plus the additional corrosion due to its electrical contact with another and more noble metal.

During this accelerated corrosion process an electric cur-rent is generated by the two metals and the magnitude of this current is related to the acceleration of the corrosion of the less noble metal beyond its normal corrosion rate. Actual corrosion cannot take place unless there is such a flow of electrical current. The magnitude of this current or the acceleration of corrosion is dependent upon basically two factors, the physical characteristics of the two metals and the physical characteristics of the electrolyte.

With respect to the physical characteristics of the two metals, two factors must be considered. First, the relative galvanic tendency between the two metals and second, the physical configuration of the two metals, namely, their relative sizes and geometric shapes. Chemical tables are available which list various metals in a series which indicate their general tendencies to form galvanic cells. From these tables, one can predict the relative tendencies between any two metals to produce galvanic corrosion.

With respect to the physical characteristics of the electrolyte, it has been found that the galvanic corrosion rate is dependent upon such factors as the concentration of salt (salinity) in the electrolyte, the temperature of the electrolyte and the pressure at any particular point in the electrolyte. Other factors also bear on the rate of galvanic corrosion but those specifically mentioned have been found to have the greatest influence.

Description and operation of the FIG. 1 embodiment FIG. la is the equivalent circuit diagram of one embodiment of a galvanic action device constructed in accordance with the present invention. This device includes a galvanic cell composed of a pair of electrodes 10 and 11. Electrode 10 may be the less noble electrode and may be of zinc while electrode 11 may be the more noble electrode and may be of gold. The choice of zinc and gold for the electrodes is made from the chemical tables of the equipment.

previously mentioned, which indicate that zinc and gold have a strong tendency to produce galvanic action.

When the galvanic cell is immersed in an electrolyte 12, such as sea water, ordinary galvanic corrosion current flows between the two electrodes through the electrolyte. After a particular amount of time, the less noble electrode completely corrodes away. The actual time required for complete corrosion is dependent upon the magnitude of the corrosion current which, in turn, is dependent upon such physical characteristics of the electrolyte 12 as temperature, salinity and pressure.

A galvanic action device constructed in accordance With the present invention also includes means for governing the corrosion current flowing between the two electrodes to compensate for changes in this current which tend to be developed by changes in the physical characteristics of the electrolyte 12. This means is shown in FIG. 1a as a bias circuit comprising a battery 13, a switch 14 and a shunt resistor 15.

As long as switch 14 is kept closed, the bias circuit applies a reverse current to the galvanic cell and effectively prevents the flow of galvanic corrosion current between the two electrodes. Thus, in the FIG. la embodiment of the invention, the compensation for changes in the galvanic corrosion current which tend to be developed by changes in the physical characteristics of the electrolyte 12, is accomplished by actually preventing galvanic corrosion current flow for a predetermined period of time.

FIG. lb shows one form which the FIG. la galvanic action device may actually take. The device shown in FIG. lb is intended to serve as a scuttling device for scuttling a floating object and will therefore be described in this enviroment. Elements in FIG. 1b corresponding to elements in FIG. la have been given the same reference numerals followed by a prime symbol.

Referring to FIG. lb, the device shown therein includes a galvanic cell composed of a zinc plug 10' corresponding to the zinc electrode 10 of FIG. 1a and a gold-plated housing 11 corresponding to the gold electrode 11 of FIG. 111. The zinc plug 10 is insulated from the gold-plated housing 11' by insulating material 16.

Metalic section 17 represents the outer surface of a floating object. The galvanic action device may be inserted into the outer surface 17 by any convenient technique such as insertion into a threaded hole as shown in FIG. 1b. A resistor corresponding to resistor 15 of FIG. la may be connected to the zinc plug 10' and the gold-plated housing 11 either by direct solder connections or by connection to solder lugs mechanically fixed to the zinc plug and the gold-plated housing. A battery 13 corresponding to battery 13 of FIG. 1a is connected across resistor 15 through a switch 14 corresponding to switch 14 of FIG. la.

The galvanic action device shown in FIG. lb may be used most advantageously as a scuttling device where the scuttling is to occur after a relatively long floating period. When the galvanic cell is exposed to the sea water 12' it tends to develop a galvanic corrosion current. However, due to the reverse current applied by the bias circuit, no such galvanic corrosion current flows. When the bias of battery 13' is removed, corrosion current is permitted to flow between the electrodes. After a particular amount of time after the reverse bias is removed the zinc plug 10 corrodes away and permits the sea water to enter the floating object through a hole 18. The galvanic cell is so designed that corrosion of the Zinc plug 10' Will take place relatively quickly in comparison to the time that the battery 13' was permitted to supply the reverse current. Although the physical characteristics of the sea water may vary, thereby affecting the time required for the zinc plug 10' to corrode away, the effect of these characteristics is minimized when considered in comparison with the overall floating period As an example, the galvanic action device shown in FIG. lb may be used in a seventy-two ihour floating period during which the bias circuit prevents galvanic corrosion with a one to three hour scuttling period after switch 14 is opened and the effect of the bias circuit is removed.

It is obvious that if the galvanic action device shown in FIG. lb is used to scuttle a piece of electronic equipment, a source of unidirectional potential within the equipment may be used instead of the battery 13. Furthermore the switch 14- would be operated auto matically with any conventional timing circuity. In an alternate arrangement, switch 14' may be eliminated and an auxiliary battery, designed to expire after the desired floating period, may be used.

Description and operation oft/1e FIG. 2 embodiment FIG. 2a is the equivalent circuit diagram of a second embodiment of a galvanic action device constructed in accordance with the present invention. This device again includes a galvanic cell composed of a pair of electrodes 20 and 21. Electrode 20 may be the less noble electrode and may again be of zinc while electrode 21, may be the more noble electrode and may again be of gold. A resistor 25, shown connected between electrodes 20 and 21 represents the small resistance of a wire which connects the two electrodes.

When the galvanic cell composed of electrodes 24 and 21 is immersed in an electrolyte 22, ordinary galvanic corrosion current flows between the electrodes through the electrolyte. After a particular amount of time, the less noble electrode 20 completely corrodes away.

The galvanic action device shown in FIG. 2a also includes means for governing the corrosion current flow between the two electrodes to compensate for changes in this current which tend to be developed by changes in the physical characteristics of the electrolyte 22. In the FIG. la galvanic action device, the corrosion current flowing between the electrodes is governed by actually preventing its flow for a predetermined period. In the FIG. 2a galvanic action device the effects due to variations in the physical characteristics of the electrolyte on the corroion current are sampled and used to regulate the corrosion current.

Specifically, means are provided for detecting changes in the physical characteristics of the electrolyte 22. This means includes a second galvanic cell composed of a pair of electrodes 21 and 23; electrode 21 being common to both galvanic cells. Electrode 23 may be the less noble electrode of the second galvanic cell and may be of magnesium while electrode 21 is the more noble electrode of the second galvanic cell. The choice of magnesium is made from the chemical tables previously mentioned which indicate that gold and magnesium have a stronger tendency to produce galvanic action than do gold and Zinc. The reason for this requirement will be explained below.

When the second galvanic cell is exposed to the electrolyte 22, it also develops a flow of corrosion current between its electrodes through the electrolyte. This corrosion current, like the corrosion current developed by the zinc-gold galvanic cell, has a magnitude dependent upon the physical characteristics of the electrolyte 22.

The corrosion current developed by the magnesiumgold galvanic cell creates a potential across a resistor 24 connected between electrodes 21 and 23. This potential varies in accordance with variations in the corrosion current of the magnesium-gold galvanic cell. As this potential is applied to the zinc-gold galvanic cell 'by way of electrode 21, its magnitude and polarity are effective as an external bias to regulate the flow of galvanic corrosion current in the zinc-gold galvanic cell and thereby com pensate for changes in the physical characteristics of the electrolyte 22 which tend to effect the corrosion current flowing in the zinc-gold galvanic cell. For example, if the physical characteristics of the electrolyte 22 tend to cause an increase in the galvanic corrosion current flowing in the zinc-gold galvanic cell, the physical characteristics would have the same effect on the corrosion current flowing in the magnesium-gold galvanic cell. In this way the magnesium-gold galvanic cell effectively detects changes in the physical characteristics of the electrolyte 22 and develops a potential across resistor 24 which is used to retard or diminish the flow of galvanic corrosion current in the zinc-gold galvanic cell accordingly. An opposite effect is developed when the physical characteristics of the electrolyte 22 tend to decrease the magnitude of the galvanic corrosion current flowing in the zinc-gold galvanic cell. Since magnesium and gold have a stronger tendency to produce galvanic action than do zinc and gold, the magnesium-gold galvanic cell is capable of developing a large enough potential to regulate the corrosion current flowing in the zinc-gold galvanic cell. However, a large enough quantity of magnesium must be used so that the magneseium electrode will not corrode away before the zinc electrode corrodes.

FIG. 2b shows one form which the FIG. 2a galvanic action device may actually take. The device shown in FIG. 2b again is intended to serve as a scuttling device for scuttling a floating object and will therefore be described in this environment. Elements in FIG. 2b corresponding to elements in FIG. 2a have been given the same reference numerals followed by a prime symbol.

Referring to FIG. 2b, the device shown therein includes a galvanic cell composed of a zinc plug 20 corresponding to the zinc electrode 20 of FIG. 2a and a gold plate or section 21' corresponding to the gold electrode 21 of FIG.'2a. The zinc plug 20' is inserted into an insulating material 26 while the gold section 21' is affixed to the insulating material. A magnesium plate or section 23 corresponding to the magnesium electrode 23 of FIG. 2a,

is also aflixed to the insulating material 26. A resistor 24- corresponding to resistor 24 of FIG. 2a is connected between the gold section 21 and the magnesium section 23 by any conventional technique. Wire 25' connecting the zinc plug 20 and the gold section 21 is represented in FIG. 2a by the resistor 25.

Metallic section 27 represents the 'outer surface of a floating object. The galvanic action device may be inserted into the outer surface 27 by any convenient technique such as a press fit with a seal between the mating surfaces of the metallic section and the galvanic action device.

. When the galvanic action device shown in FIG. 2b is exposed to the sea water, it tends to develop a galvanic corrosion current flow between the zinc plug 20' and the gold section 21 through the sea water 22. At the same time a galvanic corrosion current flow is developed between the gold section 21 and the magnesium section 23' through the sea water 22'. This second galvanic corrosion current develops a bias voltage across resistor 24' which when applied to the gold section 21', serves to regulate the galvanic corrosion current flowing between the 'zinc plug 20' and the gold section 21' in the manner previously described. After a particular amount of time, the zinc plug 20' completely 'corrodes away thus permitting the sea water 22' to enter the floating object. Since the regulation of the corrosion current is instantaneous and continuous, the galvanic action device shown in FIG. 2 may be used either for long or short floating periods.

FIG. 20 shows how the galvanic action device of FIG. 2a or 215 may be modified so as to provide a variety of scuttling periods. Since the time for complete corrosion of the zinc electrode 20 is dependent upon the size of the electrode, selection of any of a plurality of different size zinc electrodes 20a-20d, inclusive, will provide different scuttling periods. This selection is accomplished by closing any of the switches 28a-28d, inclusive, associated 'with the corresponding zinc electrodes. Once selection is made of any of the zinc electrodes, the operation of the galvanic action device of FIG. 2c is the same as the operation of the galvanic action device of FIGS. 2a or 2b.

Description and operation of the FIG. 3 embodiment FIG. 3a' is the equivalent circuit diagram of a third embodiment of a galvanic action device constructed in accordance with the present invention. This device again includes a galvanic cell composed of a pair of electrodes 30 and 31. Electrode 30 may be the less noble electrode and may again be of zinc, while electrode 31 may be the more noble electrode and may again be of gold.

When the galvanic cell is immersed in an electrolyte 32, ordinary galvanic corresion cur-rent flows between the electrodes through the electrolyte. Again, after a particular amount of time, the less noble electrode 30 completely corrodes away.

The galvanic action device shown in FIG. 3a also includes means for governing the corrosion current flow between the two electrodes to compensate for changes in this current which tend to be developed by changes in the physical characteristics of the electrolyte 32. In FIG. 3a, this means is represented by a variable resistive element 33 connected between electrodes 30 and 31. This resistive element controls the magnitude of the galvanic corrosion current developed by the galvanic cell when this cell is immersed in the electrolyte 32. Specifically, the resistive element 33, electrically connected in series with the electrodes 30 and 31, is made to vary in value in accordance with changes in the physical characteristics of the electrolyte so that as the physical characteristics change, thus tending to develop changes in the corrosion current, the resistor effectively oflsets these changes by either increasing or decreasing in value thereby decreasing or increasing the magnitude of the corrosion current.

FIG. 3b shows one form which the FIG. 3a galvanic action device may actually take. The device shown in FIG. 3b again is intended to serve as a scuttling device for a floating object and will therefore be described in this environment. Elements in FIG. 312 corresponding to elements in FIG. 3a have been given the same reference numerals followed by a prime symbol. Although the specific device shown in FIG. 3b utilizes a temperaturesensitive device to detect temperature changes in the electrolyte 32' and thereby provide compensation for such temperature changes, it is obvious that other forms of detection means, responsive to the other physical characteristics of the electrolyte, may be employed to compensate for changes in these other physical characteristics.

Specifically, the device shown in FIG, 3b includes a zinc plug 30, corresponding to the zinc electrode 30 of FIG. 3a, and a gold-plated housing 31, corresponding to the gold electrode 31 of FIG. 3a. The zinc plug 30 is insulated from the gold-plated housing 31 by insulating material 34. A carbon resistive element 33' corresponding to resistor 33 of FIG. 3a runs axially along the housing 31' and abuts against a temperature-sensitive device in the form of a bimetallic disc 35 and the zinc plug 30'. Metallic section 36 represents the outer surface of a floating object. The galvanic action device may be inserted int-o the outer surface 36 by any convenient technique, such as insertion into a threaded hole as shown in FIG. 3b.

When the galvanic action device is exposed to the electrolyte 32, ordinary galvanic corrosion current flows between the zinc plug 30 and the gold-plated housing 31' through the electrolyte. Temperature changes in the electrolyte 32' cause corresponding temperature changes in the gold-plated housing 31'. These temperature changes are effectively transferred to the bimetallic disc 35. The bimetallic disc 35 expands or contracts in response to these temperature changes and the expansion or contraction is determined by whether there is a rise or fall in temperature. The carbon-resistive element 33', capable of contracting or expanding, responds to the expansions or contractions of the bimetallic disc 35. As the carbon-resistive element 33' expands or contracts, its resistance is varied.

The path of galvanic corrosion current flow is from the zinc plug 30' though the electrolyte 32 to the goldplated housing 31', through the gold-plated housing to the bimetallic disc 35, and through the resistive element 33 back to the zinc plug 30'. Thus, as the value of the carbon-resistive element 33 changes, it causes a corresponding change in the magnitude of the corrosion current flowing through the galvanic action device.

Throughout the time that corrosion current flows through the galvanic action device, the zinc plug 34) corrodes until such time that it completely corrodes away thus permitting the electrolyte 32 to enter the floating object through holes 37. As is the case with the galvanic action device shown in FIGS. 2a and 2b, the galvanic action device shown in FIGS. 3a and 3b may be used to scuttle a floating object either after a long or short floating period since the regulation of the galvanic corrosion current is instantaneous and continuous.

A cap 31a which may be considered part of the housing 31 is provided to establish a specific ohmic resistance of the carbon resistive element 33' which corresponds to the desired floating time. In particular the cap 31a may be turned thereby changing the size of the resistive element 33' and therefore its resistance. The specific setting of the cap 31a would establish a value of resistance which would be effective to control the magnitude of the corrosion current so that complete corrosion of the zinc plug 30' would occur at the desired time assuming no changes in the physical characteristics of the electrolyte 32. However, if such changes do occur, the bimetallic disc 35 elfectively changes the value of resistive element 33' from this preset value to compensate for the changes.

While there have been described What are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. A galvanic action device comprising:

a galvanic cell which develops a corrosion current having a magnitude dependent upon the temperature of an electrolyte in which said cell is immersed;

a bimetallic disc which expands or contracts in response to temperature changes for detecting changes in said temperature;

and a carbon resistive element electrically connected in series with the electrodes of said galvanic cell and capable of varying in resistance by contracting or expanding in response to expansions or contractions of said bimetallic disc for varying the resistance through which said corrosion current flows to compensate for changes in said current which tend to be developed by changes in said temperature.

2. A galvanic action device for scuttliing a floating object in sea water after a prescribed time comprising:

a galvanic cell placed in the outer surface of said floating object and having electrodes arranged for activation by the sea water electrolyte in which said object floats for developing a corrosion current to cause a less noble electrode of said cell to corrode away, for permitting said sea water to enter and scuttle said object, the corrosion rate of said electrode being dependent upon the magnitude of said corrosion current;

:and means, including a battery arranged to apply a reverse bias potential to said cell to prevent the flow of said corrosion current and a resistive discharge path for causing said battery to expire after a predetermined period of time, said predetermined period being approximately equal to said prescribed time and substantially longer than the time required for the complete corrosion of said less noble electrode, to minimize the effect of changes in the corrosion current for scuttling said object after said prescribed time.

3. A galvanic action device for scuttling a floating object after a prescribed time comprising:

a firs-t galvanic cell having electrodes arranged for activation by a liquid in which said object floats to cause a less noble electrode of said cell to corrode away for permitting said liquid to enter and scuttle said object, the corrosion rate of said less noble electrode being dependent upon a first corrosion current developed by said first cell, said first current having a magnitude dependent upon the characteristics of the liquid;

first means for developing a second corrosion current having a magnitude dependent upon the characteristics of said liquid;

and second means responsive to said second current for developing a bias potential for regulating the flow of said first corrosion current to compensate for changes in the characteristics of said liquid which tend to affect said first corrosion current, to minimize changes in said first corrosion current for scuttling said object after said prescribed time.

4. A galvanic action device as described in claim 3, wherein said first means includes a galvanic cell for developing said second corrosion current and said second means includes a resistive element responsive to said second corrosion current for developing said bias potential across said element.

5. A galvanic action device for scuttling a floating object in sea water after a prescribed time comprising:

a. first galvanic cell, including a gold electrode and a zinc electrode, placed in the outer surface of said floating object for activation by the sea water electrolyte in which said object floats, for permitting said water to enter and scuttle said object when the zinc electrode corrodes away, the corrosion rate of said zinc electrode being dependent upon the first corrosion current developed by said first cell, said first current having a magnitude dependent upon the characteristics of the sea water electrolyte;

a second galvanic cell, including a magnesium electrode and a gold electrode, said gold electrode also being an electrode of said first cell, for activation by the sea water electrolyte in which said object floats, said second cell developing a second corrosion current whose magnitude is dependent upon the characteristics of the sea water electrolyte;

and a resistive element connected between the electrodes of said second cell and responsive to said second corrosion current for developing a bias voltage across said element, said voltage varying in accordance with variations in said second corrosion current and said voltage being applied to said gold electrode for regulating the flow of said first corrosion current to compensate for changes in the characteristics of said electrolyte which tend to affect said first corrosion current to minimize changes in said first corrosion current for scuttling said object after said prescribed time.

6. A galvanic action device for scuttling a floating object in sea water after a prescribed time comprising:

a galvanic cell placed in the outer surface of said floating object for activation by the sea water electrolyte in which said object floats, for permitting said water to enter and scuttle said object when a less noble electrode of said cell corrodes away, the corrosion rate of said less noble electrode being dependent upon a corrosion current whose magnitude is.dependent upon the temperature of the sea water electrolyte;

and a temperature sensitive variable resistive element connected between the electrodes of said cell, said resistive element being initially adjustable to determine said prescribed time, the resistance of said element additionally varying in response to changes in the temperature of said electrolyte to minimize the changes in said current for scuttling said object after said prescribed time.

7. A galvanic action device for scuttling a floating object after a prescribed time comprising: a galvanic cellhaving electrodes arranged for activation by a liquid in which said object floats to cause a less noble electrode of said cell to corrode away for permitting said liquid to enter and scuttle said object, the corrosion rate of said less noble electrode being dependent upon a corrosion current whose magnitude is responsive to characteristics of the liquid; and means for compensating for changes in said corrosion current attributable to said characteristics to minimize changes in said current for scuttling said object after said prescribed time, said compensating mean-s including a temperature sensitive variable resistive element.

8. A galvanic action device as described in claim 7,

wherein said resistive element may be initially adjusted to determine said prescribed time.

References Cited by the Examiner UNITED STATES PATENTS 2,780,993 2/1957 Goif 13690 2,826,543 3/ 1958 Sabins 204-197 2 ,868,126 1/1959 Goff et a1 13690 FOREIGN PATENTS 854,909 11/1960 Great Britain. 1,099,820 2/ 1961 Germany.

JOHN H. MACK, Primary Examiner.

. W. VAN SISE, Assistant Examiner. 

1. A GALVANIC ACTION DEVICE COMPRISING: A GALVANIC CELL WHICH DEVELOPS A CORROSION CURRENT HAVING A MAGNITUDE DEPENDENT UPON THE TEMPERATURE OF AN ELECTROLYTE IN WHICH SAID CELL IS IMMERSED; A BIMETALLIC DISC WHICH EXPANDS OR CONTRACTS IN RESPONSE TO TEMPERATURE CHANGES FOR DETECTING CHANGES IN SAID TEMPERATURE; AND A CARBON RESISTIVE ELEMENT ELECTRICALLY CONNECTED IN SERIES WITH THE ELECTRODES OF SAID GALVANIC CELL AND CAPABLE OF VARYING IN RESISTANCE BY CONTRACTING OR EXPANDING IN RESPONSE TO EXPANSIONS OR CONTRACTIONS OF SAID BIMETALLIC DISC FOR VARYING THE RESISTANCE THROUGH WHICH SAID CORROSION CURRENT FLOW TO COMPENSATE FOR CHANGES IN SAID CURRENT WHICH TEND TO BE DEVELOPED BY CHANGES IN SAID TEMPERATURE. 